Radio frequency handling device

ABSTRACT

A radio frequency signal handling device and a mobile communication device comprising such a radio frequency signal handling device. The radio frequency signal handling device comprises a first terminal interfacing external entities in the form of an input where radio frequency signals are to be received, at least one signal scaling unit having a first end where a signal provided by a terminal interfacing external entities is received, and one signal detector provided for each signal scaling unit and being connected to a second end of the corresponding signal scaling unit for detecting a signal provided by this signal scaling unit. The signal scaling unit only includes passive reactive components and comprises at least one such passive reactive component.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field radio frequencycommunication. More particularly the present invention relates to aradio frequency signal handling device and a mobile communication devicecomprising such a radio frequency signal handling device.

DESCRIPTION OF RELATED ART

In the field of mobile communication, mobile communication devices, likebase stations and mobile stations, are normally provided with a radiotransmission device comprising a power amplifier connected to an outputvia a one or more circulators, where the circulator provides isolationfor the output power.

In order to regulate the output power, it is necessary to detect theoutput power generated by the amplifier. For this reason the radiotransmission devices are provided with a directional coupler thatcouples a fraction of the power in one line into a parallel line, wherethe signal is detected to DC (rectified) from this parallel line andused for estimating the RF power level in order to regulate the outputpower.

However, these directional couplers are fairly expensive and there isalso an RF loss involved with their use.

There is therefore room for improvement when coupling a part of a signalprovided between a power amplifier and the output of a radiotransmission device.

SUMMARY OF THE INVENTION

The present invention is directed towards providing an improved radiofrequency handling device that can be obtained at reduced cost.

One object of the present invention is to provide a radio frequencysignal handling device, which includes parts that are cheap to produceand where losses may be limited.

According to the present invention this is achieved by a radio frequencysignal handling device comprising:

a first terminal interfacing external entities in the form of an inputwhere radio frequency signals are to be received,

at least one signal scaling unit having a first end where a signalprovided by a terminal interfacing external entities is received, and

one signal detector provided for each signal scaling unit and beingconnected to a second end of the corresponding signal scaling unit fordetecting a signal provided by this signal scaling unit,

wherein the signal scaling unit only includes passive reactivecomponents and comprises at least one such passive reactive component.

The radio frequency signal handling device may with advantage beprovided in a radio transmission device such as a base station or amobile station.

The invention has the following advantages. The signal scaling unit ischeap and simple to produce, which means that the total cost of thedevice may be reduced. It may here be provided as a part of a circuitboard. The signal scaling unit furthermore has a fairly low loss, whichis of advantage in some application where the invention may be used. Thesignal scaling unit is also insensitive to temperature change.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, steps or components, but does not preclude the presence oraddition of one or more other features, steps, components or groupsthereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail in relationto the enclosed drawings, in which:

FIG. 1 shows a circuit diagram of a radio frequency signal handlingdevice according to a first embodiment of the present invention in theform of a radio transmission device,

FIG. 2 shows a circuit diagram of a radio frequency signal handlingdevice according to a second embodiment of the present invention in theform of a radio transmission device,

FIG. 3 shows a circuit diagram of a radio frequency signal handlingdevice according to a third embodiment of the present invention in theform of a radio transmission device,

FIG. 4 shows a circuit diagram of a radio frequency signal handlingdevice according to a fourth embodiment of the present invention in theform of a signal attenuating device,

FIG. 5 schematically shows two mobile communication devices, one basestation and one mobile station, communicating with each other, whereeach may include a radio frequency signal handling device according tothe invention, and

FIG. 6 shows a front view of a mobile station in the form of a cellularphone.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention relates to a radio frequency handling device forhandling radio frequency signals. A radio frequency handling device whenprovided in the form of a radio transmission device normally has a poweramplifier feeding a generated signal in a connection to an antenna via adirectional coupler and a pair of circulators. Here the circulatorsfunction to isolate the generated signal from load variations and fromsignals received by the antenna. The circulator furthermore reduces thebackward intermodulation. The directional coupler on the other handcouples a fraction of the signal to a parallel connection where thesignal fraction can be detected and used for control purposes. Such adirectional coupler normally has a coupling factor of about 20-30 dB.Backward reflections of this signal are not coupled. However thedirectional coupler is a quite expensive component and may alsointroduce fairly high losses that it would be advantageous to reduce.

One aspect of the present invention is therefore directed towardsproviding the same functionality as the traditional radio transmissiondevice, but where the above mentioned problems associated with thedirectional coupler have been addressed.

A radio frequency handling device in the form of a radio transmissiondevice 10 is according to a first embodiment of the present inventionshown in a circuit diagram in FIG. 1. The radio transmission device 10includes an input I on which it receives a radio frequency signal from asignal generating unit (not shown). This input is connected to the inputof a power amplifier PA, the output of which is connected to a firstterminal of a first circulator CIR1. The first circulator CIR1 has asecond terminal connected a first terminal of a second circulator CIR2and a third terminal connected to ground via a first matching resistorR1. The second circulator CIR2 has a second terminal connected to afirst output O1 of the radio transmission device 10 and a third terminalthat is also connected to ground via a second matching resistor R2. Thefirst output O1 is connected to an antenna A. A signal scaling unit 12,indicated by a dashed box, has a first end that is also connected to thefirst terminal of the first circulator CIR1 and a second end connectedto the input of a signal detector DET as well as to ground via a thirdmatching resistor R3. The detector DET, which is also indicated by adashed box, here includes a diode D, the input of which is connected tothe second end of the signal scaling unit 12 and the output of which isconnected to a second output O2 of the device 10. The detector DET alsoincludes a fourth resistor R4 connected between the second output O2 andground. The signal scaling unit is finally made up of a first inductorL1 connected in series with a first capacitance C1. The input I and thefirst output O1 are here both terminals interfacing external entities,i.e. entities that are not part of the radio frequency signal handlingdevice, like the above mentioned signal generating unit and the antennaA.

The functioning of the radio transmission device 10 is as follows. Theradio transmission device 10 receives a radio frequency signal on theinput I that is to be transmitted via the antenna A connected to thefirst output O1. Therefore the power amplifier PA amplifies this signal,which is then fed via the two circulators CIR1 and CIR2 to the antennaA. The two circulators CIR1 and CIR2 function to reduce radio signalsreceived via the antenna A, so that these signals do not disturb theamplifier PA. They also create a constant load to the amplifier PA aswell as provide a sufficient enough isolation for reflective wavesbecause of a good match using the first and second matching resistancesR1 and R2. A circulator typically has a VSWR (Voltage Standing WaveRatio) of 1.15. Such signals and reflective waves are instead provideddown to ground via the first and second resistors R1 and R2. Thusreverse waves are stopped from influencing the amplifier.

Because of this it is possible to provide the signal scaling unit 12 forcoupling a fraction of the amplified radio frequency signal in a verysimple way. It does thus not separate forward and reverse radiofrequency waves as the known directional coupler. However this is notnecessary as the circulators CIR1 and CIR2 provide enough isolation frombackward waves. Therefore the signal scaling unit 12 of this firstembodiment can be kept very simple and also efficient regarding theattenuation of the wave as compared with a directional coupler. Here thefirst capacitor C1 and first inductor L1 are chosen in size so that theyprovide an attenuation of about 15-25 dB of the signal in the frequencyrange in which the radio transmission device is to operate, which may bearound 450 MHz. It should be realised that this frequency is a merespecific example and that any suitable radio frequency can be usedinstead. Here the Q-value of the inductor L1 influences the attenuation.The higher the Q-value is the smaller the losses will get. Losses forthe whole unit 10 and the loss in the inductor L1 get smaller for higherQ-values. The signal scaling unit 12 has a certain variation in theattenuation in the frequency range in which the radio transmissiondevice 10 is to operate. In the present example it is less than 1 dB forthe frequency range associated with the 450 MHz frequency. However thisvariation may be removed when the output power control loop iscalibrated in production. The passive reactive elements L1 and C1 arefurthermore fairly insensitive to temperature changes, which may be ofadvantage in mobile communication that is carried out outdoors inchanging weather conditions. The signal scaling unit 12 here couples apart of the amplified signal to the detector DET, where it may bedetected and output via the second output O2 and used in controlling theamplification of the amplifier PA. This signal may thus be used in aknown way in order to control the amplifier stage. The third matchingresistance R3 is dimensioned to match the detector DET and typically hasa value of about 50Ω. Also the first and second matching resistances R1and R2 are dimensioned for a suitable matching of the circulators CIR1and CIR2, which is normally the same value of 50Ω.

The signal scaling unit is not limited to be provided between acirculator and the amplifier. It can be used for other purpose.

One such variation according to a second embodiment of the presentinvention is described in relation to FIG. 2. FIG. 2 shows essentiallythe same elements as FIG. 1. However, here a signal scaling unit 14 inseries with a fifth matching resistor R5 is connected in parallel withthe second matching resistor R2 for the second circulator CIR2. Thesignal scaling unit 14 here comprises a second capacitor C2 and a secondinductor L2 selected in the same way as the first capacitor C1 and firstinductor L1 were selected. The detector DET is here also connected tothis signal scaling unit 14 in the same way as it was connected to thesignal scaling unit 12 in FIG. 1. What is measured here is not theoutput power; it is rather the power reflected to the second circulatorCIR2, which may include signals received and reflected by the antenna A.

It should here be realised that the two embodiments may be combined,i.e. be provided in a device that both measures the transmitted power aswell as reflected power from the Antenna A. This allows thedetermination of the VSWR for the connected antenna in an efficient andcost-effective manner.

Another variation according to a third embodiment of the presentinvention is shown in FIG. 3, which is essentially the same as FIG. 1.The only difference is that there is provided a filter F between thesignal scaling unit 12 and the detector DET. The filter F here serves tofilter out harmonics of signals that are outside of the desiredfrequency range in order to provide a better detection.

It is furthermore possible to use the signal scaling unit as anattenuator instead of an ordinary power attenuator. An example of thiswhen the signal handling device is a signal attenuating device 16according to a fourth embodiment of the present invention is shown inFIG. 4. Here there is an input I, which is connected to a signal scalingunit 18, which has the same configuration as the signal scaling units ofFIG. 1-3, i.e. is provided with an inductor L3 in series with acapacitor C3. The signal scaling unit 18 is in turn connected to adetector DET of the same type as described in relation to the first tothird embodiments, which in turn is connected to a fourth output O4.Here 50Ω matching resistances R6 and R7 are connected between the signalscaling unit 18 and the input I and between the signal scaling unit 18and the detector DET, respectively. The input I is here supplied with anRF signal, which gets attenuated by the signal scaling unit 18 and thendetected by the detector DET, which provides the detected signal on theoutput O4. The signal scaling unit 18 together with the powerterminations R6 and R7 provides good attenuation at a lower price thanordinary attenuators for a narrowband frequency range when the RF-linesand terminations have a good VSWR. There is furthermore a lower powerloss in the scaling unit 18 compared with a resistive attenuator.

The signal scaling unit according to the present invention can be variedin a number of ways. It may include only one passive reactive componentinstead of two, either an inductor or a capacitor. However an inductoris presently preferred, because the tolerances of the capacitors oftoday are inadequate for the frequency ranges of interest. However, ifsuch tolerances can get improved in the future, also a single capacitormay be of interest. These passive reactive components are further morevery simple and cheap to produce. They can for instance be provided as apart of a circuit board. This thus allows the device to become veryeconomical to produce. The radio transmission device can also be varied,in that it may be possible to have only one circulator. It should alsobe realised that the detector is not limited to diode detectors, but maybe any RF detecting unit that transforms an RF energy level to a DCvoltage.

The radio frequency signal handling device according to the presentinvention may be provided in either a base station or a mobile stationor in both. FIG. 5 schematically shows one such base station 20communicating with a mobile station 22 in a wide area network N. Hereboth these are provided with a radio frequency signal handling deviceaccording to the invention. The mobile station 22 may here also be acellular phone, which is shown in FIG. 6.

Although the present invention has been described in connection withspecific embodiments, it is not intended to be limited to the specificform set forth herein. Rather, the scope of the present invention islimited only by the accompanying claims.

The invention claimed is:
 1. A radio frequency signal handling devicecomprising: a first terminal interfacing external entities in the formof an input where radio frequency signals are to be received, at leastone signal scaling unit having a first end where a signal provided by aterminal interfacing external entities is received, and one signaldetector provided for each signal scaling unit and being connected to asecond end of the corresponding signal scaling unit for detecting asignal provided by this signal scaling unit, wherein the signal scalingunit only includes passive reactive components and comprises an inductorand capacitor in series, and wherein the signal scaling unit is furtherconnected to a matching resistance at the connection point to the signaldetector for matching the scaling unit to the detector, and wherein theradio frequency signal handling device comprises at least twocirculators connected between the amplifier and the output.
 2. A radiofrequency signal handling device according to claim 1 further comprisinga filter between the signal scaling unit and the detector.
 3. A radiofrequency signal handling device according to claim 1 wherein it is aradio transmission device that further comprises an amplifier connectedto the input for receiving said radio frequency signals to betransmitted, a second terminal interfacing external entities in the formof an output be connected to an antenna for transmitting these radiofrequency signals.
 4. A radio frequency signal handling device accordingto claim 3, wherein one signal scaling unit is with its first endconnected between the amplifier and a circulator in order to receive asignal provided by the input and couple a fraction of this signal afterbeing amplified to a connected detector.
 5. A radio frequency signalhandling device according to claim 3 wherein one signal scaling unit iswith its first end connected between a circulator and a matchingresistance in order to receive a signal provided by the output andcouple a fraction of this signal to a connected detector.
 6. A radiofrequency handling device according to claim 1 wherein it is a signalattenuating device and the first end of the signal scaling unit isdirectly connected to the input in order to receive a signal from thisterminal.
 7. A radio frequency handling device according to claim 6,further comprising a matching resistance connected between ground andsaid input.
 8. A mobile communication device comprising a radiofrequency signal handling device according to claim
 1. 9. A mobilecommunication device according to claim 8, wherein it is a base station.10. A mobile communication device according to claim 8, wherein it is amobile station.